I want to mount the personal challenge of proving myself in the NRL Gareth Ellis

The 26-year-old will be the only British player in the NRL.

"This has been a life-changing decision based on my personal career goals to play at the elite level in both Super League in the UK and the NRL," he said.

Ellis joined Leeds from Wakefield in 2005 and has made 93 appearances for the Rhinos and won 19 Lions caps.

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He was part of Britain's 2005 and 2006 Tri-Nations squads as well as the 2007 team which defeated New Zealand.

Ellis, who was named in the World XIII last year, has been hailed as "the world's best second rower" on the Wests Tigers website.

He insisted his decision would not affect his displays for the Rhinos over the course of Super League XIII.

"Leaving Leeds will be a massive wrench and my focus for the rest of the 2008 season will be to help my colleagues on the playing and coaching staff to achieve the club's objectives of winning the World Club Challenge, the Challenge Cup and the Grand Final," he said.

"Then I hope to receive the invitation to play a part in England's bid to lift the World Cup in Australia in the autumn.

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"And I then want to mount the personal challenge of proving myself in the NRL with the Wests Tigers, who have impressed me with their ambition to repeat their Grand Final success of 2005.

"Because of the significance of a major new three-year contract, the Rhinos and interested clubs in Australia wanted an early decision.

"Continuing to serve the Rhinos would have been my choice if staying in the UK, having thoroughly enjoyed the Headingley experience since joining them from Wakefield Trinity in 2005.

"However, my partner Rachael and I, plus our respective families, are excited by the prospects of a change of lifestyle, coupled with my personal challenge on the field, especially at this stage of my rugby league career."

There are currently no British players in the NRL after Richard Mathers left the Gold Coast Titans to move to Wigan late last year.

The last British forward to play in the league that is generally regarded as the toughest in the world was Warrington star Adrian Morley, who spent six successful seasons with Sydney Roosters.

Wests coach Tim Sheens believes that Ellis can make a positive impact at the Australian club.

"Gareth is probably playing his best football. He has experience and brings a great attitude, not only as a trainer but off the field as well," he said.

"Gareth will need to have that as he will be a big name here in Australia as one of the first Englishmen to come into the NRL in some years at Test level